(1) Field of the Invention
This invention relates to a four-way switching valve, and more particularly to a four-way switching valve which carries out switching of refrigerant lines when the cooling and heating operation mode is switched in a heat pump-type heating and cooling system for an automotive vehicle.
(2) Description of the Related Art
In a heating and cooling system for an automotive vehicle, a refrigerating cycle is employed when cooling operation is performed, and when heating operation is performed, engine coolant is used as a heat source. Recently, however, due to the improvement in combustion efficiency of the engine, the temperature of the coolant does not rise high enough to obtain sufficient heating temperature in winter. For this reason, there is an increasing need for a system which can perform both cooling and heating. In a heating and cooling system of this kind, it is necessary to reverse the direction of flow of a refrigerant flowing through an internal heat exchanger and an external heat exchanger, as the system is switched between cooling and heating operations. The flow of the refrigerant is switched by a four-way switching valve.
FIG. 18 is a block diagram showing the arrangement of a heating and cooling system using the four-way switching valve.
The heating and cooling system is comprised of a compressor 101, a four-way switching valve 102, an external heat exchanger 103, a decompressor 104, an internal heat exchanger 105, and an accumulator 106. The four-way switching valve 102 includes four ports A to D. The port A of the four-way switching valve 102 is connected to a delivery side of the compressor 101, the port B is connected to the external heat exchanger 103, the port C is connected to the internal heat exchanger 105, and port D is connected to the accumulator 106.
During the cooling operation, the four-way switching valve 102 is switched such that the port A and the port B is communicated with each other and the port C and the port D is communicated with each other, as indicated by solid lines in FIG. 18. Therefore, a high-temperature and high-pressure refrigerant compressed by the compressor 101 is guided into the port A of the four-way switching valve 102, and sent from the port B to the external heat exchanger 103, where the refrigerant is caused to undergo heat exchange and condensed, and then by the decompressor 104, the refrigerant is adiabatically expanded to a low-temperature and low-pressure refrigerant. The internal heat exchanger 105 causes the low-temperature and low-pressure refrigerant to undergo heat exchange with warm air in the vehicle cabin and evaporate. Then, the refrigerant flows through the port C and the port D of the four-way switching valve 102 to enter the accumulator 106, where it is caused to undergo gas/liquid separation, followed by returning to the compressor 101.
On the other hand, during the heating operation, the four-way switching valve 102 is switched such that the port A and the port C communicate with each other and the port B and the port D communicate with each other, as indicated by broken lines in the figure. Therefore, the high-temperature and high-pressure refrigerant compressed by the compressor 101 is sent through the port A and the port C of the four-way switching valve 102, to enter the internal heat exchanger 105, where it is caused to undergo heat exchange with cool air in the vehicle cabin to heat the same. The refrigerant condensed by the internal heat exchanger 105 is adiabatically expanded by the decompressor 104 to the low-temperature and low-pressure refrigerant. Then, the external heat exchanger 103 causes the refrigerant to undergo heat exchange to evaporate, and then the refrigerant is guided through the port B and the port D to flow into the accumulator 106, where it is caused to undergo gas/liquid separation, followed by returning to the compressor 101.
As described above, the four-way-switching valve 102 can switch the operation mode of the heating and cooling system, by changing over the flow path of refrigerant.
As the four-way switching valve 102, there has been proposed a four-way switching valve in Japanese Patent Application No. 2001-183291 filed by the present applicant. The four-way switching valve is configured such that a first valve and a third valve for opening and closing passages from a port A into which a high-pressure refrigerant is introduced, to a port B or a port C, and a second valve and a fourth valve for opening and closing passages from the port B or the port C to a low-pressure port D are made separate and independent. The first valve and the second valve, and the third valve and the fourth valve are driven by a first piston and a second piston, respectively, and at the same time two solenoid valves are provided for selectively guiding part of the high-pressure refrigerant introduced into the port A, to pressure-regulating chambers for the first and second pistons.
This enables the two solenoid valves to guide a high-pressure fluid in the port A into the pressure-regulating chamber for the first piston or that for the second piston in a switching manner, thereby making it possible to switch between a first state in which the port A communicates with the port B, and the port C communicates with the port D, and a second state in which the port A communicates with the port C, and the port B communicates with the port D.
However, although the conventional four-way switching valve is configured such that the high-pressure refrigerant is selectively introduced into one of the respective pressure-regulating chambers for the first and second pistons to thereby drive the first to fourth valves, the pressure of one of the chambers into which the high-pressure refrigerant is not introduced is reduced by leaking it to the low-pressure port D via a corresponding one of respective clearances between the first and second positions and the cylinders for accommodating the pistons, whereby the first or second piston is returned to a switching position thereof in the first or second state. Therefore, the four-way switching valve suffers from the problem that the leakage of refrigerant from the pressure-regulating chambers to the low-pressure port D results in degraded refrigerating power of the heating and cooling system, although the amount of leakage is very small.
The present invention has been made in view of the above points, and an object thereof is to provide a four-way switching valve free from leakage of refrigerant. To achieve the above object, there is provided a four-way switching valve for switching between a first state in which a fluid introduced into a first port is discharged to a second port and the fluid introduced into a third port is discharged to a fourth port, and a second state in which the fluid introduced into the first port is discharged to the third port and the fluid introduced into the second port is discharged to the fourth port. The four-way switching valve comprising a combination of a first three-way switching valve for carrying out a switching operation to cause the second port to communicate with the first port or the fourth port and a second three-way switching valve for carrying out a switching operation to cause the third port to communicate with the fourth port or the first port.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.